Apparatus of the coffee machine type for preparing beverages, which use packed or unpacked portions of foods substance(s) are very widespread among individuals and even among communities, commercial premises and businesses. The preparation principle is based on the extraction of the substance by the passage through this substance of a quantity of cold or hot liquid under high pressure, typically a pressure several times higher than the atmospheric pressure. The packed portions may be partially rigid capsules or flexible, hermetically sealed or partially open bags, or even filter doses.
An example of a capsule is described in patent EP 0 512 468 B1. An example of a bag is described in patent EP 0 602 203 B1.
Such extraction systems present many advantages. On the one hand, the individual packages are easy to use and do not require batching the quantity of coffee to be placed in the machine. The user places a capsule, a dose of ground coffee or other portions in the machine, then presses a button to start extraction. On the other hand, the individual packages are batched to deliver a beverage, such as coffee, having the desired characteristics such as sufficient character, flavour, foam or other important attributes. If they are impermeable, they also usually preserve the freshness of the substance better up to the time of extraction. Finally, the preparation conditions, such as the temperature, pressure, extraction time, are easier to control; this guarantees relatively controlled and constant quality to the consumer.
An example of an extraction method is described in patent EP 0 512 470 B1.
In order to extract a beverage under pressure from these portions, of the capsule or other type, it is necessary to use a relatively powerful water pump such as a piston pump. These pumps use the mains electric power. They are also rather noisy during extraction due to vibrations.
It is also difficult to move these preparation apparatus, as on a trolley or simply by carrying them, because of their electrical connection. In fact, it would be an advantage to make these apparatus more mobile in order to propose beverages in locomotion facilities like the train, airplane, or in certain premises such as cinemas, theatres, or in public places such as beaches, parks, poolsides and other public or private places, along country walks, campsites or in other situations.
French certificate of addition FR 94.925 relates to a portable coffee percolation apparatus that comprises a receptacle provided with a deformable membrane which is deformed by a pressurised gas from a cylinder, to send the pressurised water into a nozzle comprising a spout receiving the coffee to be percolated. However, the device and its membrane are only configured to eject the fluid under the gas pressure into the nozzle, but they are not configured to fill the chamber with liquid. In order words, the membrane only performs the role of a filling “piston”. The membrane does not have elastic return properties suitable for creating a suction of the liquid into the chamber from an external liquid source. The filling is carried out manually through a plug. Such an arrangement raises serious safety questions for an apparatus for preparing hot beverages, because the chamber is maintained under gas overpressure, and even under slight overpressure, hot or boiling water could be uncontrollably expelled outside the chamber when the chamber plug is opened. Furthermore, such an apparatus is impractical because of the obligation of manual filling. Thus, to provide satisfactory self-contained operation, the chamber must be sufficiently large (several liters); this demands the use of excessive volumes of gas.
Patent application WO 99/02081 proposes a coffee machine, more precisely a mobile machine, in which the pressure required to extract the ground coffee is generated by compressed air. The water for preparing the coffee is kept in a thermally insulated container. The water may be heated by electric heating elements. This solution presents the advantage of producing the extraction pressure by a self-contained means, such as a gas cylinder, placed below the machine. The machine can be installed on a trolley with the gas cylinder installed in a trolley compartment provided for the purpose.
However, such a device presents a number of drawbacks. In fact, in this invention, the gas in the cylinder communicates with the hot water tank directly. This means that the entire volume of the tank is kept under constant pressure, of about several bar.
It is therefore necessary to provide a large capacity tank to withstand the pressure; this raises problems of design and manufacture, in order to guarantee sufficient safety. If the tank is accidentally fractured, it may explode and cause damage. In case of leaks, hot water jets may escape and cause accidents such as burns. Moreover, the design of the tank is limited in the choice of materials, and it cannot use brittle materials with low mass heat capacity such as glass, for example. Finally, prolonged contact of the gas with a large reserve of water under high pressure can also cause the uncontrolled dissolution of gas in the water; this can therefore deteriorate the taste of the beverage, for example, by making it slightly sparkling or sour.
Patent application WO 2004/014205 relates to a device for preparing a beverage using hydraulic means of the piston type to push the liquid into the extraction chamber in which the capsule is installed in order to extract the beverage under pressure. The piston is actuated by a pressurised gas. However, it is necessary to guarantee sealed operation of the system over a large number of cycles, which is liable to raise problems.
Co-pending European application 03026792.6 relates to a device for preparing a beverage in which the water is introduced into a feed chamber and expelled under pressure by a gas, which is itself introduced into the chamber. The chamber is filled by hydrostatic effect from a tank. The chamber can advantageously be installed in the tank itself to avoid heat losses. However, the filling of the chamber is relatively slow; this raises problems in the preparation of several beverages in succession, particularly for large volumes of beverages delivered.
It is therefore an object of the present invention to propose an apparatus for preparing beverages that is quieter than the apparatus using pumping systems actuated by electrical energy.
It is a further object of the invention to propose an apparatus that is suitable for mobile or portable use, while avoiding the drawbacks of the solution of patent application WO 99/02081.
In particular, one of the objects is to propose an apparatus with sufficient self-contained liquid capacity but in which only a limited volume of liquid is pressurised, in order to reduce the risks and drawbacks associated with the maintenance of a large capacity tank under permanent pressure. A further object is to propose a simple, sealed structure that is reliable during prolonged use. A further object is to reduce the filling time in order to increase the capacity to serve several beverages in succession in a minimum of time. A further object is to reduce the heat or cold losses of the apparatus, in particular to improve its mobility.